Diamond left Sale on Tuesday after 10 years for personal reasons and without him the English side struggled to cope with their French opponents, for whom Louis Carbonel was outstanding.
France fly-half Carbonel contributed 16 points as Toulon's tries came from wing pair Gabin Villiere and Ramiro Moyano, but Sale rallied from 26-0 down.
Marland Yarde and Sam Phillips grabbed consolations, but Sale's poor discipline and line-out struggles cost them.
Sale competed on an equal footing for the opening quarter and it took until the 21st minute for Carbonel to open the scoring. In the first five minutes the Sharks were indebted to superb defence from Cobus Wiese stopping what looked like being a certain home try.
That moment aside, Sale were not afraid to have a go. AJ MacGinty would have been disappointed to not be successful with a penalty attempt. Wiese then did well to dance down the touchline.
Sale were clearly keen to move the ball from side to side, but their attempt to do so saw former New Zealand superstar Ma'a Nonu smash Simon Hammersley in midfield. Toulon won the penalty through some fine breakdown work from Villiere and Carbonel did not miss as he made it 6-0.
Hammersley did brilliantly to reclaim MacGinty's restart, but more magic from Carbonel created the game's first try. The fly-half chipped ahead, collected his own kick, and sent Villiere away to score, with Carbonel converting.
Both sides were warned by referee Frank Murphy after a dust-up just before half-time. Toulon felt Carbonel had been taken out at a ruck, but it was handbags.
The Toulon pitch was cutting up badly, but after Toulon won a scrum penalty, Carbonel sent his team to the break 16-0 up with the last kick of the half.
Carbonel started the second period as he ended the first, with a penalty, and then saw his loosehead prop Jean-Baptiste Gros break clear.
Sale lost Jono Ross to a head injury assessment while Toulon's giant second row Eben Etzebeth went the same way after the two players collided.
South Africa's World Cup-winning scrum-half Faf De Klerk came on to try and turn the tide back Sale's way, but he could not stop Toulon's second try.
Replacement hooker Christopher Tolofua barged his way through and found Sergio Parisse.
The veteran Italian was tackled by De Klerk but produced a miracle offload to wing Moyano and Carbonel added the extras.
Sale hit back through Yarde and it was a fine try. Sam James kicked ahead with his left foot and Sam Dugdale did brilliantly to collect and send Yarde over the line, and MacGinty converted.
All of a sudden Sale were dangerous, helped by the impetus of De Klerk and James from the bench. They grabbed a second try when their forwards drove forward and De Klerk found lock Phillips who scored between the posts.
MacGinty kicked the simple goal, but there was no further score.